The present invention relates to a combined cycle power plant, which is a combination of a steam turbine power facility with a gas turbine power facility.
In recent years, there has been a greater increase in demand for an improved thermal efficiency in a thermal power facility. Especially, there has recently been a demand for development of a high thermal efficiency system utilizing the existing facilities in view of difficulty in acquiring the site of a new facility and decrease in construction costs. It is said that conversion of a conventional power plant into a combined cycle power generation system is the most effective way in order to provide such a high thermal efficiency.
With respect to measures for remodeling the existing conventional thermal power facility into the combined cycle power system, there have been known an exhaust gas re-combustion type power plant as shown in FIG. 10 and a heat recovery type power plant as shown in FIG. 11.
In the exhaust gas re-combustion type power plant as shown in FIG. 10, a combustion boiler, which is applied in an existing steam turbine power unit, is utilized as it is. More specifically, the existing steam turbine power unit A is provided generally with a steam turbine power facility 3 having a steam turbine 1 and a generator 2, a combustion boiler 4 for supplying steam to the steam turbine 1, a steam condenser 5 (which may be called merely condenser hereinlater) for condensing an exhaust gas from the steam turbine 1, a condenser pump 6 for supplying condensed water (i.e., condensate) to the combustion boiler 4 and the other components. A gas turbine power unit B, which is additionally provided in the above-mentioned steam turbine power unit A, is provided with a gas turbine power facility 10 having a combustor 7, a gas turbine 8, a generator 9 and the other components. A high-temperature gas, which still contain sufficiently large amounts of oxygen and unburned fuel discharged from the gas turbine 8 in sufficient amounts, is introduced as air for boiler combustion into a furnace of the combustion boiler 4 to burn fuel xe2x80x9cFxe2x80x9d and an exhaust gas after combustion is discharged from a stack 11. Such an exhaust gas re-combustion type power plant has advantageous features of permitting to enhance a boiler-efficiency and achieve heat recovery of a boiler-exhaust gas through heat exchange between the boiler-exhaust gas and a boiler-feedwater.
In the heat recovery type power plant as shown in FIG. 11, a heat recovery steam generator (HRSG) 12 is provided in place of the combustion boiler used in the existing steam turbine power unit so as to cause production of steam in the existing steam turbine power unit with the use of an exhaust gas from the gas turbine 8. The structural components as shown in FIG. 11 are identical to those in FIG. 10. Accordingly, the same reference numerals as in FIG. 10 are given to the identical components in FIG. 11 and description thereof is omitted. Such a heat recovery type power plant has advantageous features of permitting to introducing a high-temperature gas discharged from the gas turbine 8 into the heat recovery steam generator 12 to generate steam so as to drive the steam turbine 1 by the thus generated steam.
The above-described types of the power plant, however, has provided the following problems.
The exhaust gas re-combustion type power plant as shown in FIG. 10 provides a low improvement-value in efficiency of about 5% as a relative value. For example, there is assumed that a single 240 MW gas turbine of 1300xc2x0 C. class is provided in an existing 500 Mw boiler/turbine facility to remodel such facility into a combined cycle power generation system having the same plant power output. The thermal efficiency of the existing plant is assumed as 40%. When the existing system is remodeled into the exhaust gas re-combustion power plant under such conditions, although the combination of the gas turbine as additionally provided and the existing steam turbine ensures the plant power output of 500 MW, the thermal efficiency is about 42%, thus leading to improvement merely of about 5% as a relative value.
When the existing system is remodeled into the heat recovery type power plant as shown in FIG. 11, there are problems of small power output and impossibility of an independent operation only by the existing boiler/turbine facility. More specifically, the system is composed of the gas turbine as additionally provided, the heat recovery steam generator as additionally provided and the existing steam turbine, and in such arrangement, the existing combustion boiler is removed. In such a case, the thermal efficiency is about 50%, leading to increase in a relative value by 25%, while the power output of 380 MW can merely be ensured, leading to decrease in power output by about 30%. The impossibility of the independent operation only by the existing boiler/turbine facility makes it impossible to carry out a power generation operation during a regular inspection of the gas turbine. Coal, fuel oil and the like are applied as fuel for the existing combustion boiler. Continuous application of such fuels cannot cope with demands for an improved high-thermal efficiency and reduced costs.
An object of the present invention, which was made in view of such circumstances, is to provide a combined cycle power plant, which permits, when an existing steam turbine power facility is remodeled to the combined cycle type, to ensure plant power output that is equal to that of the existing steam turbine power facility prior to remodeling, provide a remarkably improved thermal efficiency and carry out an independent operation of the existing facility with the use of the existing conventional boiler and steam turbine.
This and other objects of the present invention can be achieved according to the present invention by providing, in one aspect, a combined cycle power plant, comprising:
a gas turbine power facility;
a heat recovery steam generator into which an exhaust gas is introduced from the gas turbine power facility;
a steam turbine power facility having a steam turbine mounted to a shaft different from a shaft on which the gas turbine power facility is mounted;
an existing boiler for supplying steam to the steam turbine power facility;
a system for introducing steam, which is generated in the heat recovery steam generator and the existing boiler, into the steam turbine of the steam turbine power facility through steam lines, which extend from the heat recovery steam generator and the existing boiler and are then joined together; and
a system for causing a line, which is arranged on a downstream side of a steam condenser provided in the steam turbine power facility, to branch off into feedwater lines, and supplying condensate condensed by the condenser into the heat recovery steam generator and the existing boiler.
In this aspect, the steam lines extending from the heat recovery steam generator and the existing boiler to the steam turbine and the feedwater lines extending from a condensed water pump of the steam condenser to the heat recovery steam generator and the existing boiler are provided with valves, respectively, to permit selection of any one of three operation patterns of: a simultaneous power generation operation of the gas turbine power facility and the steam turbine power facility utilizing the steam generated in both the steam generator and boiler; a simultaneous power generation operation of the gas turbine power facility and the steam turbine power facility utilizing only the steam generated in the heat recovery steam generator, while the existing boiler not being in operation (shut-down); and a single power generation operation of only the steam turbine power facility utilizing only the steam generated in the existing boiler, while shutting down the operation of the gas turbine.
The heat recovery steam generator is provided with a low-pressure economizer and there is provided a system for returning at least a part of feedwater, which is heated by the low-pressure economizer, to feedwater or condensed water on an upstream or downstream side of a deaerator provided on a condensed water line.
A recirculation line is arranged for returning the condensed water from the downstream side of the deaerator to the condenser to control oxygen concentration of the feedwater.
The steam condenser is provided, therein, with a deaerating device to control oxygen concentration of the feedwater.
The power plant may be further comprise a control device for controlling load of all the systems in accordance with an operation of at least one of the gas turbine, the steam generator and the boiler.
A single common stack is arranged for discharging the exhaust gas from the heat recovery steam generator and the exhaust gas from the existing boiler.
A first stack is arranged for discharging the exhaust gas from the heat recovery steam generator and a second stack is arranged, independently from the first stack, for discharging the exhaust gas from the existing boiler.
According to another aspect of the present invention, there is also provided a combined cycle power plant comprising:
a gas turbine power facility;
a heat recovery steam generator into which an exhaust gas is introduced from the gas turbine power facility;
a steam turbine power facility provided with a steam turbine mounted on a shaft which is different from a shaft on which the gas turbine power facility is mounted, the steam turbine power facility including high, intermediate and low pressure turbines;
an existing boiler for supplying steam to the steam turbine power facility;
a system for introducing a steam, which is generated in the heat recovery steam generator and the existing boiler, into the high-pressure turbine of the steam turbine power facility through steam lines, which extend from the steam generator and the boiler and are then joined together;
a system for distributing the steam, which has done work in the high-pressure turbine so as to reach a low temperature, to the heat recovery steam generator and the existing boiler through reheat lines and for supplying the steam, which has been reheated by the heat recovery steam generator and the existing boiler to a high-temperature reheat steam, to the intermediate and low pressure turbines in a combined state; and
a system for causing a line, which is arranged on a downstream side of a condenser provided in the steam turbine power facility, to branch off into feedwater lines, and supplying condensed water condensed by the condenser into the heat recovery steam generator and the existing boiler.
In modified embodiment in this aspect, the steam lines extending from the heat recovery steam generator and the existing boiler to the steam turbine and said feedwater lines extending from a condensed water pump of the condenser to the heat recovery steam generator and the existing boiler are provided with valves, respectively, to permit selection of any one of three operation patterns of: a simultaneous power generation operation of the gas turbine power facility and the steam turbine power facility utilizing the steam generated in both the steam generator and boiler; a simultaneous power generation operation of the gas turbine power facility and the steam turbine power facility utilizing only the steam generated in the heat recovery steam generator, while the existing boiler being not operated; and a single power generation operation of only the steam turbine power facility utilizing only the steam generated in the existing boiler, while shutting down the operation of the gas turbine.
A steam line is arranged for introducing the steam generated from the heat recovery steam generator into a first stage of the low pressure turbine or a middle stage thereof of the steam turbine power facility or a middle stage of the intermediate pressure turbine.
An extraction line is arranged for introducing the steam from the lower pressure turbine into a feedwater heater, which is disposed in a condensation system of the steam turbine power facility, and a line for introducing the steam generated from the heat recovery steam generator is connected to the extraction line.
The heat recovery steam generator is provided with a low-pressure economizer and there is provided a system for returning at least a part of feedwater, which is heated by the low-pressure economizer, to feedwater or condensed water on an upstream or downstream side of a deaerator provided on a condensed water line.
A recirculation line is arranged for returning the condensed water from the downstream side of the deaerator to the steam condenser to control oxygen concentration of the feedwater.
The steam condenser is provided, therein, with a deaerating device to control oxygen concentration of the feedwater.
At least one of reheat lines, which introduce the low temperature steam from the high-pressure turbine to the heat recovery steam generator or the existing boiler, is provided with a distributing valve for adjusting a distribution ratio of the steam having the low temperature.
The combined cycle power plant may further comprises a control device for controlling load of all the systems in accordance with an operation of at least one of the gas turbine, the steam generator and the boiler.
A single common stack is arranged for discharging the exhaust gas from the heat recovery steam generator and the exhaust gas from the existing boiler.
A first stack is arranged for discharging the exhaust gas from the heat recovery steam generator and a second stack is arranged, independently from the first stack, for discharging the exhaust gas from the existing boiler.
In a further aspect of the present invention, there is provided a combined cycle power plant comprising:
a gas turbine power facility;
a heat recovery steam generator into which an exhaust gas is introduced from the gas turbine power facility;
a steam turbine power facility provided with a steam turbine mounted on a shaft which is different from a shaft on which the gas turbine power facility is mounted, the steam turbine power facility including high and low pressure turbines;
an existing boiler for supplying steam to the steam turbine power facility;
a system for introducing steam, which is generated in the heat recovery steam generator and the existing boiler, into the steam turbine through steam lines, which extend from the steam generator and the boiler and are then joined together;
a system for supplying feedwater condensed by a condenser to the low pressure state by branching off lines at an outlet portion of a condensed water pump provided for the steam turbine power facility and for supplying feedwater supplied to the heat recovery steam generator to a low pressure turbine through a low pressure economizer, a low pressure drum and a low pressure superheater; and
a system for supplying feedwater, which is supplied to the existing boiler, to a feedwater pump through a deaerator, branching off lines at an outlet stage of the feedwater pump, supplying the feedwater to a high pressure stage of the heat recovery steam generator and the existing boiler and supplying the feedwater supplied to the heat recovery steam generator to the high pressure turbine, after joining to steam generated from the existing boiler, through a high pressure economizer, a high pressure drum and a high pressure steam superheater.
According to the present invention described above, it is possible to ensure, when an existing steam turbine power facility is remodeled into a combined cycle type, the plant power that is equal to that of the existing steam turbine power facility prior to remodeling, provide a remarkably improved thermal efficiency and carry out an independent operation of the existing facility with the use of the existing existing boiler and steam turbine, thus providing such useful effects.
Further, as for the fuel, it is also possible to use various kinds of fuel such as LNG (liquid natural gas), fuel oil and coal, leading to reduction in running cost.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.